In a conventional DC power supply, the electrolytic capacitors are commonly used as the energy storage and filter capacitors because the electrolytic capacitors have greater capacitance than other types of dielectrics (such as ceramic, mica, glass, paper, oil or the like), but they also have shortcomings, such as undesirable frequency and temperature characteristics, shorter lifespan, and greater leakage current. When terminal voltage is greater than specification of the capacitor, electrolytic solution would be gasified and then blasted. Depletion of the electrolytic solution also causes attenuation and degradation of the capacitors. Their utilization is constrained in application fields where higher reliability is required for a prolonged duration. The conventional design of power supply generally adopts a plurality of electrolytic capacitors coupled in parallel to get greater capacitance, but such a design causes maintenance problem in practice.
The reliability for power supply systems and charging equipment is always one of the important issues in electric power quality. During the DC power supply system being in operation, capacitor degradation could cause unstable power supply and power interruption that result in production shut down of petrochemical or nuclear power plants, paralysis of financial markets (such as computer crash in financial transaction market), chaos of public transportation systems, and even risk people's life and threaten financial conditions and environments.
Moreover, capacitor degradation also reduces filtering effect and increase voltage ripple at the DC side to further damage energy storage device. The energy storage device is expensive and very important in an Uninterruptable Power System (UPS). In order to protect the energy storage device, the priority is to take care of the capacitors. In recent years, rapid advances of technology have spawned myriad of electronic instruments and precision equipment, thus stability of UPS becomes even more important. During operation of UPS, detection of capacitor degradation is performed by first switching the power supply to other power source and making the UPS in an OFF condition, or detection has to be regularly implemented. All these cannot automatically perform capacitor degradation alarm. How to detect capacitor degradation while the DC power supply system is in normal operation without affecting load apparatus at the output side of the UPS is an issue not yet fully resolved and still a goal pursued by the present invention.